Okay true. He is a fucking angsty teenager with issues. If you were said angsty teen, would you jack off over a comatose girl? As a dude, wouldn't you want to get in a gigantic fucking robot, and smash 'evil' stuff? That's every dude's dream, and one of the biggest reasons why the giant robot genre is so popular. And even then, if you wanted out of all that crazy bullshit, wouldn't you just be like, "If you don't go in, we'll have rei do it!" "...Yes let's have rei do it. Or alter it so that an adult can use it instead of fucking teenagers."

I understand that it is symbolic, and that can be quite good in it's own right. Though when one removes the symbolism subtext, and you get an unrelatable main character, that is a total puss, with no constant reason to be there. Seriously, anyone like that character should just run the fuck away. He does run the fuck away, but he always comes back because of *insert bullshit reason related to the episode here*.

The jacking off part is a bit weird, I just think he was aroused and jacking off to his number 1 love interest. As a dude I would probably control a robot to save freaking humanity, and that's probably his reason too, and the fact that his dad would give him recognition for it. The last reason he did it was because he saw how wounded rei was, giving him motivation to do something good for once.
Adults cant use it because of the whole idea that the robot harbors the soul of a parent. Preferably the mother. It could probably been a grandmother and a mother instead, but since Shinji's mom was the one that figured it out then she felt it had to be her, for Asuka she was from a different place we dont know anything about, for all we know it was random that it was her and not a grown person.